The Sodor and Mainland Railway originally attempted to cut a tunnel through the Ballahoo Ridge, but it collapsed during construction, resulting in the railway only running trains between Kirk Ronan and Ballahoo.
After its founding in 1915, the North Western Railway constructed its own tunnel in order to reach Vicarstown. The NWR was built as a strategic railway in time of emergency. Speed and cheapness of construction were paramount, so a single line bore only was cut, and the Up and Down lines gauntletted. While work was in progress a section midway collapsed leaving two tunnels (the Western - 1 mile, and the Eastern, or Henry’s - 450 yards).
The tunnel gained its nickname in 1922 after Henry refused to come out, claiming the rain would spoil his "lovely green paint with red stripes" and was subsequently bricked up. A second bore was cut alongside to provide a double line and Henry was eventually let out sometime in 1923 to help with the express. In 2011, the tunnel collapsed but was repaired in time for the unveiling of the Thin Clergyman's bust at Tidmouth.
In the first season of the television series, Henry stopped in the tunnel (like in the Railway Series). In the fourth season, an elephant blocked the tunnel and Henry had to take workmen to clear it. In the thirteenth season, while painted pink; James hid in the tunnel. In the nineteenth season, Thomas hid from the Fat Controller in the tunnel after he lied about an accident.
- Henry's Tunnel has had numerous modifications throughout the years:
- Season 1:
- One tunnel bore had two tracks and the other bore had one track.
- Season 4:
- The numerous switch tracks and the siding disappeared.
- Season 7:
- Season 8:
- Both bores had two tracks.
- Season 13:
- The tunnel appeared to get shorter as you could see through it.
- Blue Mountain Mystery:
- The tunnel was seen in a flashback and it only had one track in each bore.
- The Adventure Begins:
- Two switch tracks were added in front of the signal box.
- The tracks became slightly curved on the opposite of the tunnel.
- Season 1: